1. Field of the Invention
The present invention relates to a developing device in an electrophotographic image forming apparatus such as printers.
2. Description of the Related Art
There have been known various types of developing devices in electrophotographic image forming apparatuses. As a typical example, there has been a developing device, wherein there are provided a magnet member, a developing sleeve rotating around the magnet member and a developer restricting member confronting the developing sleeve, and developer is held on the developing sleeve by a magnetic force of the magnet member and is transported to a developing region by the rotation of the sleeve, while restricting a transportation rate or amount by the restricting member.
In the developing device of this type, clogging often occurs at the restricting member due to causes such as solidification of the developer and/or paper dust, in which case the developer is not transported through the clogged portion, resulting in a void in an image.
For example, the Japanese Laid-Open Patent Publication No.60-146276 has proposed a developing device, in which a magnet member is provided with a magnetic pole portions (forming an identical magnetic polarity part) which are repulsive to each other are disposed between a developer restricting member and a developing magnetic pole of the magnet member.
This developing device of the prior art is designed to correct irregularity in a thickness of a developer layer by flight of the developer at the identical magnetic polarity part in the magnet member, and to prevent the void in the image, which may be caused by the clogging at the restricting member, by filling the void with the flown developer. Naturally, a possibility of the clogging at the restricting member increases as a space between the restricting member and the surface of the developing sleeve decreases.
In the developing device of the prior art, however, the flight of the developer at the identical magnetic polarity part is irregular, so that heights of developer chains are also irregular along an axial direction of the developing sleeve. This causes irregular density in a developed solid image.